The Study Of Thermal Interference And Outlet Tube Insulation Feasibility Of The Single U-Shaped Ground Heat Exchanger

With the vigor increase of the energy saving and emission reduction, the application of terrestrial heat are paid more and more attention as an important kind of clean energy. Ground Source Heat Pump is an energy efficient air conditioning system of making use of underground shallow geothermal resources, through the heat pump cooling (heating) cycle, we achieve the cooling of air conditioning for the summer and the heating for the winter. Due to its highly efficiency and stability, energy saving and environmental protection, low running costs and other advantages, it has absorbed widespread attention and research.How to improve the performance of U-tube heat exchanger is always the key and difficulty of Ground Source Heat Pump system research. The heat transfer of the U-tube heat exchanger and the soil is an extremely complex process, there are many influencing factors, the thermal interference occurred between the two U-tubes and shallow soil is a very important factor. Thermal interference, to some extent, reduces the efficiency of the U-tube heat exchangers.This thesis takes an actual ground source heat pump project of the single U-shaped ground heat exchanger about a real project as the experimental subject, analyzed the heat transfer in cooling period by using the test data of temperature distribution about the engineering backfilling materials in well. On the basis, we established a three-dimensional heat exchange model, then we verified the validity of the model using the measured data. Subsequently, we made further simulation analysis of the thermal interference on summer cooling conditions using the validated model and discussed the influence of the drilling depth, velocity of U-tube, the thermal conductivity of backfill material, Pipe spacing of U-tube on the U-tube heat exchanger capacity. In the single influencing factors, we identified the turning point of the fluid along the tube length, be the lowest temperature point. If taking heat preservation measures of the corresponding length of the U-tube after the lowest temperature point, we can avoid the heat interference coming from the inlet tube and topsoil, try to reduce unnecessary heat loss and improve heat transfer efficiency of U-tube system. Being justified the effectiveness of taking heat preservation measures about the return branch pipe.In summary, we did the further research of thermal interference of the single vertical U-tube heat exchangers in cooling period and the feasibility of heat preservation, the results show that the thermal interference between the two U-tubes and shallow soil do exist, taking a certain length of heat preservation on the return branch pipe can reduce this part of the heat loss. However, in different thermal interference factors, the heat preservation length of return branch pipe and the effect is different, the heat preservation length is not as long as better, and it does not mean that taking heat preservation measures will be able to have satisfactory results.